It is our goal to characterize, in vitro, the relationship between the physiologic effect of angiotensin II (AII) and its binding to proposed receptor molecules. Our initial experiments will use adrenal glomerulosa cells of the rat as model system. Saturable binding of AII and aldosterone production will be measured under identical experimental conditions in each pool of cells prepared. These parameters will be measured with respect to the time of incubation and with respect to the effect of drugs which have been reported to increase or to decrease saturable AII binding. Subsequent experiments will test the hypotheses that AII receptors in various target organs are different and that receptor properties may be altered by various experimental conditions. Toward this end, we will measure, in vitro, several binding properties of the receptor: the apparent equilibrium association constant, K, for AII; the number of binding sites, n; and the apparent dissociation constant of several equilibrium competitive inhibitors of AII. The binding properties will be estimated in adrenal glomerulosa cells and aorta of rats subjected to experimental conditions reported to alter the responsiveness of target organs to AII or obtained from the appropriate controls. Experimental treatment will consist of either dietary sodium restriction or induction of various forms of hypertension: renal hypertension, desoxycorticosterone-induced hypertension, or genetic hypertension. The apparent equilibrium association constant, K, and the number of binding sites, n, will be estimated from Scatchard plots of steady state binding data. The apparent dissociation constant of equilibrium competitive AII antagonists will be estimated by calculating pA2 values from dose-response curves generated by AII in the absence or presence of antagonists.